Fig. 1

On a true AP glenohumeral X-ray, A the humeral head is circled, and the center of rotation is marked. B Measuring the ACEA formed with the first drawn superiorly from the center of the humerus parallel to the glenoid surface and the second drawn from the center of the circle to the lateral-most aspect of the acromion edge. C Measuring the GTA angle formed by the first drawn parallel to the diaphyseal axis that passes through the humeral head center of rotation; the second drawn connects the superior border of the humeral head to the superolateral edge of the greater tuberosity